TAILIEUCHUNG - Chapter 062. Principles of Human Genetics (Part 29)

Population Genetics In population genetics, the focus changes from alterations in an individual's genome to the distribution pattern of different genotypes in the population. In a case where there are only two alleles, A and a, the frequency of the genotypes will be p2 + 2pq + q2 = 1, with p2 corresponding to the frequency of AA, 2pq to the frequency of Aa, and q2 to aa. When the frequency of an allele is known, the frequency of the genotype can be calculated. Alternatively, one can determine an allele frequency, if the genotype frequency has been determined. Allele frequencies vary. | Chapter 062. Principles of Human Genetics Part 29 Population Genetics In population genetics the focus changes from alterations in an individual s genome to the distribution pattern of different genotypes in the population. In a case where there are only two alleles A and a the frequency of the genotypes will be p2 2pq q2 1 with p2 corresponding to the frequency of AA 2pq to the frequency of Aa and q2 to aa. When the frequency of an allele is known the frequency of the genotype can be calculated. Alternatively one can determine an allele frequency if the genotype frequency has been determined. Allele frequencies vary among ethnic groups and geographical regions. For example heterozygous mutations in the CFTR gene are relatively common in populations of European origin but are rare in the African population. Allele frequencies may vary because certain allelic variants confer a selective advantage. For example heterozygotes for the sickle cell mutation which is particularly common in West Africa are more resistant to malarial infection because the erythrocytes of heterozygotes provide a less favorable environment for Plasmodium parasites. Though homozygosity for the sickle cell gene is associated with severe anemia and sickle crises Chap. 99 heterozygotes have a higher probability of survival because of the reduced morbidity and mortality from malaria this phenomenon has led to an increased frequency of the mutant allele. Recessive conditions are more prevalent in geographically isolated populations because of the more restricted gene pool. Approach to the Patient Inherited Disorders For the practicing clinician the family history remains an essential step in recognizing the possibility of a hereditary component. When taking the history it is useful to draw a detailed pedigree of the first-degree relatives . parents siblings and children since they share 50 of genes with the patient. Standard symbols for pedigrees are depicted in Fig. 62-9. The family history .

• Y học thường thức
• Principles of Human Genetics
• bệnh học và điều trị
• bài giảng bệnh học
• tài liệu y khoa
• Harrisons Internal Medicine
• Biological information
• Lecture Genetics
• Human genetics
• Modern genetic techniques
• Mendels principles
• Mendels principles of heredity